standardize on 'basic' debug log level for all gnupg bits #1439
remove hard-coded path to libpinentry, its JNI so it should be found easily
switch String.isEmpty() to String.length() == 0 to support android-8 (2.2) #1239
add ContentProvider for searching by keyId and email, similar to APG's #1442

We can't actually make our ContentProvider work for apps that expect to use
APG's ContentProvider because we can't claim APG's permission for this. So
instead, this is just a similar, tho expanded, API.